The proposed experiments will define how afferents from active muscle (muscle reflex), the cardiopulmonary receptors and the arterial baroreceptors interact to produce the cardiovascular response (both cardiac and vasomotor), to dynamic exercise in the conscious dog. The primary hypothesis is that reductions in blood flow to working muscle activates muscle afferents (Group III and IV chemoreceptors) which in turn initiate reflex adjustments in the cardiovascular system to restore muscle blood flow back towards pre-occlusion levels. Techniques are described for producing graded blood flow reductions to active muscle, while concurrently assessing cardiovascular effector responses including blood pressure, heart rate, cardiac output and blood flow in various visceral circulations (renal, mesenteric). The experiments outlined in this proposal will examine the nature of the reflex arising from active muscle, both in the normal dog and in animals exercised when cardiac performance is severely limited. The relationship between perfusion of active muscle and the accompanying systemic cardiovascular response(s) is determined in the normal animal and after eliminating input from arterial baroreceptors and/or cardiac receptors. This proposal utilizes techniques for selective cardiac afferent denervation in conjunction with arterial baroreceptor denervation procedures. Together they provide a stable chronic dog preparation which allows multiple comparisons of responses to be made over extended periods of time. The experimental approaches, developed in this proposal, will provide valuable new data to determine the afferent mechanisms involved in control of the circulation during exercise in normal animals and in those with severe limitations of cardiac performance. Importantly, it evaluates the influence of muscle afferents in control of both cardiac function and visceral blood flow during severe exercise, data not presently available for the conscious dog model.